Optical brightener composition for paper



United States Patent 3,211,665 OPTICAL BRIGHTENER COMPOSITIGN FOR PAPER William Allen, North Plainfield, and Robert Frank Gerard, Manville, N..l., assignors to American Cyanamid Company, Stamford, Conn., a corporation of Maine No Drawing. Filed Dec. 3, 1962, Ser. No. 241,518

Claims. (Cl. 252301.2)

This invention relates to an improved brightener composition and to a process for brightening paper therewith. More particularly, it relates to an improved method for the application of a class of diaminostilbene triazine brighteners to paper stock by tub size or size press methods using N,N,N,N-tetrakis(2-hydroxypropyl)ethylenediamine in combination with said diaminostilbene triazine brighteners.

Various diaminostilbenedisulfonic acid triazine com pounds (hereinafter referred to as DAS triazines), because of their ability to fluoresce, have previously been used as brighteners to neutralize or mask the natural yellowish tinge of cellulose, for the purpose of rendering the paper made from it, optically bright or white, in appearance. From a commercial viewpoint, most DAS triazine brighteners are insufficient in especially one respect. They do not show their normal blue fluorescence when applied under acidic conditions such as are encountered in conventional paper-making processes, e.g., during pulp heating or sizing operations. In the pulp beater, for one reason or another, the pH often falls as low as about 4. In some instances when brighteners are added to strongly acidic paper pulp, they actually intensify, rather than obcsure, the yellow tinge of the pulp. This cannot be overcome by increasing the brightener concentration since, in such cases, the greater the amount of brightener, the greater the yellowness of the pulp.

While highly acid conditions are normally to be avoided during paper manufacture, nevertheless, due to factors sometimes beyond control, acidity does develop and must be anticipated so that something can be done to abate adverse consequences to the brightener. One approach to the problem is to use a brightener composition which is stable to acid conditions. It is an object of the present invention to provide such a composition. Other objects will be made apparent by a consideration of the following detailed description.

The present invention is based on the discovery that brighteners of the DAS triazine series as defined below, may be applied to paper during the pulp beating step, or with especial effectiveness, during tub size or size press steps, with improved results even under extreme acidity, if they are applied in the presence of N,N,N,N'-tetrakis (2-hydroxypropyl)ethylenediamine.

Brighteners which may be applied by the process of this invention are represented by the formula:

wherein R is a sulfonic acid group in the meta or para position. The preferred brightener for application in the process of the invention is the brightener of the above formula wherein R is a sulfonic acid group attached to the phenyl ring in the para position.

It is surprising that such good results are obtained using the specific ethylenediamine as defined, since even with an amine such as triethanolamine, which is sometimes used in brightener applications, yellow discoloration results under highly acidic conditions, and this material is therefore unsatisfactory.

While the present invention is applicable to beater operations, especially in tub size (or size press) applicatrons and at low pHs, does its great advantage become evident. Thus, in tub size applications at pHs of about 5.5 or even lower, using a brightener of Formula I in combination with the above-defined tetra substituted ethylenediamine, superior results are obtained with no yellow discoloration, whereas, using the same brightener with no amine agent or with another amine agent such as trietihanolamine, yellow discoloration results to such a degree that the product is unsatisfactory. Moreover, at higher pHs, such as around pH 7 where the yellow discoloration problem is minimized, improved brightening effects are obtained when using the diamine brightener combination of the invention, instead of only the brightener of Formula I per se.

The DAS triazine brightener and N,N,N',N,-tetrakis(2- hydroxypropyl)ethylenediamine may be added to the size mixture separately; or it is often more convenient to make up an aqueous stock solution of the brightener containing the requisite amount of the ethylenediamine. Using such a composition, the brightener and diamine may be added to the size mix simultaneously. Any sizing method useful in papermaking may be modified and improved hereby. Tub size (or size press) procedures are examples of such methods. In tub size applications, the sizing is applied to the surface of the paper sheets using rollers or doctor blades, the amount of sizing applied to, or retained by, the paper being controlled by the pressure of the rolls or the blade. Starch is an example of a material normally used in a sizing operation although other materials may also be used. In practicing the present invention, a difinite amount of diamine should be associated with the DAS triazine brightener of Formula I. At least about one part by weight of the diamine per part of real brightener should be used. Up to about five parts by weight may be used, but this is not necessary and be comes uneconomical. In preferred practice, about 1.5 to about 2.5 parts of diamine per part of real brightener are used. An aqueous stock solution of the brightenerdiamine combination may have about 5 to 25 weight percent of the DAS triazine brightener and about one to five times as much of the diamine.

For sizing applications, using starch as the size, for example, the aqueous sizing mixture may have about one to about four percent of the DAS triazine brightener and about one to about five times that amount of the diamine, based on the weight of the size. Thus, if the aqueous size mixture contains about 4 to 8 percent, preferably 6 percent starch, it should also have about 0.05 to 0.2% of the DAS triazine brightener and about 0.05 to about one percent of the diamine.

The following examples are presented to illustrate the present invention.

Example 1 To 50 ml. of a 12% starch solution at 200 to 206 F. is added 50 ml. of an aqueous solution containing 0.16 part of a DAS triazine brightener of the Formula II:

SOsH

(HOCH CHM T 2 and 0.4 part of the diamine of the Formula III:

OH en oll-CH With stirring, the pH of the mixture is adjusted to 5.5 by the addition of aluminum sulfate. The solution is heated at 140 F. and it is then applied to paper stock, making a uniform drawdown with a No. 12 equilizer rod. The stock sheet is then immediately placed in an air oven at 200 F. for one minute and then conditioned in a constant humidity room for one hour.

The dried sheet of paper is observed for brightness in north daylight. It has no yellow discoloration. Under UV light it shows full chromaticity.

When the above procedure is repeated identically except for use of an equal amount of triethanolamine, the resulting sheet of paper shows yellow discoloration in north daylight and is much less chromatic when observed under UV light.

Example 2 The procedure of Example 1 is repeated except that sufiicient aluminum sulfate is added to bring the pH of the mixture to 4.5. The resulting sheet of paper appears bright under north daylight.

When triethanolamine is substituted in the above procedure, the resulting sheet of paper appears much more yellow under north daylight and under UV light is much less chromatic when compared to the sheet prepared in Example 2.

Example 3 N noonicnmrhf TNH-QCH:

N iv 1 sour Q wherein R is a member selected from the group consisting of m-SO H and p-SO H radicals; and (b) the amine of the formula:

H CHQ(EHCH3 said mixture containing from about one to five parts of (b) for each part of (a). 2. The process of claim 1 wherein R is a p-SO H radical.

3. The process of claim 2 wherein between 1.5 and 2.5

parts of (b) are used for each part of (a).

4. The process of claim 1 wherein said contact is effected in the presence of a paper sizing material.

5. The process of claim 4 wherein said sizing material is starch.

6. A composition suitable for neutralizing the yellowness in natural cellulose consisting essentially of an aque- 5 ous mixture of (a) a brightener of the formula:

N (HOCH CI'Iz)zN( NH- CH: N N 50.11 R Ni wherein R is a member selected from the group consisting of m-SO H and p-SO H radicals; and (b) the amine of the formula:

on (|)H 2O om-otL-on, CHz-CHCH /NCIIzCH3-N cH -o HoH, CHZ(IJHCH3 OH OH said mixture containing from about one to five parts of (b) for each part of (a).

7. The composition of claim 6 wherein R is a p-SO H radical.

. 8. The composition of claim 6 wherein between 1.5 and 2.5 parts of (b) are present for each part of (a).

9. A composition suitable for neutralizing the yellowness in natural cellulose consisting essentially of an aqueous mixture of (c) a paper sizing material; said mixture containing about 0.05 to 0.2 weight percent of (a), about 0.05 to 1 weight percent of (b) and about 4 to 8 weight percent of (c).

10. The composition of claim 9 wherein (c) is starch.

References Cited by the Examiner UNITED STATES PATENTS 2,697,118 12/54 Lundstedt et al. 260-584 3,012,971 12/61 Gessner et a1. 252301.2 3,025,242 3/62 Seylor 25230l.2

OTHER REFERENCES Rose, The Condensed Chemical Dictionary, Reinhold Pub. Corp., New York, 1961, pp. 372 and 388.

TOBIAS E. LEVOW, Primary Examiner.

7 MAURICE A. BRINDISI, Examiner. 

1. IN THE PROCESS OF NEUTRALIZING THE YELLOWISH TINGE OF NATURAL CELLULOSE FIBERS BY CONTACTING SAID FIBERS WITH A BRIGHTENER COMPOSITION, THE IMPROVEMENT WHICH COMPRISES USING AS SAID BRIGHTENER COMPOSITION, AN AQUEOUS MIXTURE OF (A) A BRIGHTENER OF THE FORMULA:
 6. A COMPOSITION SUITABLE FOR NEUTRALIZING THE YELLOWNESS IN NATURAL CELLULOSE CONSISTING ESSENTIALLY OF AN AQUEOUS MIXTURE OF (A) A BRIGHTENER OF THE FORMULA: 